1. Field of the Invention
The present invention relates to a reinforcing bar binding machine which feeds a wire of a wire reel, winds the wire around a reinforcing bar in a loop shape, and then twists and binds the wire, a wire reel attached to a reinforcing bar binding machine body and having information display means of the type or the like of a wire reel, and a rotational information detecting method which detects the rotational information from an information detection region of the wire reel.
2. Background Art
In a conventional reinforcing bar binding machine, a wire reel around which a wire is wound is held at a rear portion of the binding machine, the wire is pulled out by feed gears of a wire feeding device from the wire reel and delivered forward when a switch is turned on and a trigger is operated, the wire is supplied in a loop shape from a curved portion of the tip of a guide arm and wound around a reinforcing bar, and then, a portion of the loop is held, and twisted, and turned by a twisting hook, thereby binding the reinforcing bar. As one which automatically adjusts torsion torque of the wire of the reinforcing bar binding machine, there is a device in which a side surface of the wire reel is provided with a display means which displays the type of a wire, the display means is detected by a detecting means provided in the reinforcing bar binding machine, the type of the wire is determined on the basis of a result detected by the detecting means, and the torsion torque is automatically adjusted (for example, JP-A-2005-194847).
By providing a portion of the wire reel in a convex shape, and detecting this convex shape by a contact type sensor provided in the binding machine body, this device performs detection of absolute rotation of the wire reel. Moreover, aside from this, a portion of a black recess formed at a side surface of the wire reel is provided with white projections, and rotation detection by a reflective photosensor provided in the binding machine body is also performed. By setting the interval of signal by two sensors to 90°, the number of the white projections per one rotation of the wire reel is detected, and feed/torsion control suitable for the wire diameter/wire type of consumable goods is made.
However, there are the following problems in the detection by the reflective photosensor.
1) The bottom surface of the black recess of the wire reel is not a flat. Some stepped portions are formed. Accordingly, in a case where the white projections are detected by the reflective photosensor, all height differences within the recess as well as the white projections may be detected due to characteristics of the photosensor. Accordingly, as shown by a line 70 in FIG. 28, erroneous detection occurs since output signals by the photosensor change and a voltage is not returned, and erroneous detection easily occurs even by attachment of sand or dust.
2) There is a variation in the sensitivity of the photosensor, and while this is taken into consideration, the area of the white projections should be increased in order to switch on/off of the sensor reliably. For this reason, the shape of the wire reel is also largely restricted, and it is difficult to increase resolution. Additionally, since the number of white projections is also restricted, various kinds of information cannot be given.
3) In the conventional sensor, as shown by a line 71 in FIG. 28, the signal interval becomes 90°. Therefore, the ranges where rotation cannot be detected immediately after start of rotation of the wire reel and immediately before stop of rotation thereof are respectively 90°. Therefore, the error of rotation detection of 180° at the maximum per 1 binding occurs. This error becomes the detection error of feed amount of about 50 mm even at the last stage of rotation of the wire reel where an exact wire feed amount can be detected. Meanwhile, when the feed amount becomes 40 mm shorter than a predetermined feed amount, twist off at the time of binding easily occurs. Accordingly, when correction of the feed amount is performed from the rotational amount of the wire reel, only the resolution at which a decrease in the feed amount of at least 40 mm is detected is required. Accordingly, by the existing sensor, precise detection of rotation of the wire reel at the time of wire feed cannot be performed, and a decrease in wire feed amount caused by wear of the feed gears cannot be detected.